I noticed that the clock of my kitchen oven got late, it lost about three minutes in just two weeks. It surprised me since this clock has been very accurate for two years.
I got the answer from a Hacker News thread: oven clocks often don't have a quartz but instead count how many times the tension goes to zero, assuming that at 50 Hz it reaches zero 100 times per second.
This works well when the frequency is stable, but currently Europe suffers from a deficit in energy production slowing the grid down. Thus clocks getting late.